American scientists who reviewed 35 recent
in vivo studies of ginseng concluded that the quality of clinical
research in this area is too low to serve as convincing evidence
of ginseng's efficacy in improving human physical performance
(Bahrke et al., 2000). The papers reviewed were animal
and clinical studies utilizing a variety of ginseng species (including
Korean [Panax ginseng C.A. Meyer, Araliaceae]; American
[P. quinquefolius L.]; Vietnamese [P. vietnamensis
Ha et Grushv]; and eleuthero, a.k.a. Siberian ginseng [Eleutherococcus
senticosus (Rupr. ex Maxim.) Maxim, Araliaceae]) published
between 1994 and 1999. Sixteen evaluated ginseng's effect on exercise
performance in humans. The recent animal studies reviewed bolstered
earlier findings that ginseng significantly increases aerobic
endurance in rats and mice, apparently by altering the way the
body uses fuel. One new finding indicates that ginseng also may
boost animals' exercise performance by increasing muscle mass.
Treatment with P. ginseng was associated with a positive
effect on cognitive function in older rats and reduced signs of
anxiety in rats and mice. However, human trials of ginseng often
fail to confirm the positive effects observed in animal studies.
The reviewers speculate that poor compliance rates, lower doses,
or the failure of animal researchers to employ double-blind designs
may explain this pattern.

The review focused on 16 clinical trials
of ginseng's effect on exercise performance, most of which involved
athletes or fit, healthy participants. Eleven studies utilizing
various ginseng species reported that ginseng had no significant
effect on any measures of psychological or physiological response
to exertion. One study reported improved endurance, recovery time,
and reaction time in people taking ginseng, but failed to present
a statistical analysis of significance. The four remaining studies
(two of which used a ginseng/fenugreek [Trigonella foenum-graecum
L., Fabaceae] combination and two of which used E. senticosus)
reported that ginseng treatment caused significant increases in
aerobic performance, muscular strength, and endurance. Ginseng
did not reduce blood lactate levels during exercise in any of
the studies.

According to the review authors, these
mixed results might be attributable to variations among ginseng
species as well as the quality of ginseng preparations used, which
may be affected by the plant's age and growing environment, season
of harvest, and post-harvest processing. In the studies reviewed,
researchers failed to use standardized preparations, failed to
report these data, or relied on manufacturers' standardization
claims instead of their own chemical analyses. The reviewers stressed
that these and other problems are significant limitations to the
credibility and repeatability of these studies. The authors also
claim that recent analysis has suggested that methylxanthines
such as caffeine, theophylline, and theobromine are present in
ginseng in widely varying amounts and may influence study results.
Ginseng does not contain caffeine. The research cited actually
shows that some commercial ginseng supplements tested positive
for caffeine, presumably because the product was formulated to
contain caffeine. The authors of the review studies conducted
no assays to determine levels of methylxanthine compounds in the
test formulations they used.

In summary, the authors were highly critical
of the current body of ginseng research, citing "numerous statistical
and design problems" and "various methodological problems such
as inadequate sample size and lack of double-blind, control and
placebo paradigms." A number of trials used ginseng in combination
with other ingredients (for example, herbs, vitamins, or high
levels of alcohol) and/or did not specify the treatment dose,
duration, or preparation. The reviewers assert that future research
must address these issues before any conclusions may be drawn
about ginseng's effects on human physical performance.